This application is based on Japanese patent applications No. 9-309037 filed on Nov. 11, 1997, and No. 9-309038 filed on Nov. 11, 1997, the entire contents of which are incorporated herein by reference.
a) Field of the Invention
The present invention relates to a solid-state image pickup device, and more particularly to techniques of transferring electric charges accumulated in a solid-state image pickup device and techniques of processing an image signal picked up with a solid-state image pickup device.
b) Description of the Related Art
FIG. 18 is a schematic diagram showing the structure of a conventional image signal processing apparatus.
A solid-state image pickup device 51 has a pixel field 52 and a horizontal transfer path 53. The pixel field 52 has photodiodes disposed two-dimensionally and a plurality of vertical transfer paths.
An image 55 is picked up in the pixel field 52. Each photodiode converts a light signal of the picked-up image 55 into electric charges which are passed from the photodiode to the vertical transfer path wherein the electric charges are transferred in the vertical direction.
The horizontal transfer path 53 receives electric charges of one row (a train of pixels in the horizontal direction) from a plurality of vertical transfer paths and transfers the electric charges in the horizontal direction. An amplifier 54 amplifies the electric charges transferred from the horizontal transfer path 53 and outputs them to a processing unit 61. Next, the horizontal transfer path 53 receives electric charges of the next row from a plurality of vertical transfer paths and transfers them in the horizontal direction. Similar operations are repeated thereafter to output two-dimensional image signals to the processing unit 61.
A flow of electric charges representative of image information will be described. Electric charges read from photodiodes are first passed to the vertical transfer path which is a primary transfer path for transferring electric charges in the vertical direction. Next, the electric charges are passed to the horizontal transfer path which is a secondary transfer path for transferring electric charges in the horizontal direction.
The charge transfer described above corresponds to an image scan like a raster scan. First, electric charges are scanned in the horizontal direction or main scanning direction MD, and then scanned in the vertical direction or sub-scanning direction SD. Electric charges of the next row are again scanned in the main scanning direction (horizontal direction) MD. These scans are repeated to scan the two-dimensional image 55.
The amplifier 54 outputs analog electric signals to the processing unit 61. The processing unit 61 has an A/D converter, a D/A converter, and the like to convert the analog electric signals into digital electric signals which are processed in a predetermined manner and converted into analog electric signals to be output to a monitor 64.
The monitor 64 displays an image 65 through raster scanning. More specifically, scanning in the image horizontal direction or main scanning direction MD is first performed and then scanning in the vertical direction or sub-scanning direction SD is performed. Scanning in the main scanning direction (image horizontal direction) MD is again performed for the next line. These scans are repeated to display the two-dimensional image 65 on the monitor 64.
The main scanning direction MD and sub-scanning direction SD of the solid-state image pickup device 51 are equivalent to the main scanning direction MD and sub-scanning direction SD of the monitor 64.
FIGS. 19A and 19B are schematic diagrams illustrating conventional interlace-scanning image signal processing. The interlace-scanning forms one frame by two fields, an A field FA and a B field FB. In FIGS. 19A and 19B, the A field FA is shown as a hatched area.
FIG. 19A is a schematic diagram illustrating the interlace-scanning of a solid-state image pickup device 51 which corresponds to the solid-state image pickup device 51 in FIG. 18 turned upside down. The A field FA constituted of a collection of odd rows is first scanned on the solid-state image pickup device 51, and then the B field constituted of a collection of even rows is scanned. One row is a train of pixels to be scanned in the main scanning direction (image horizontal direction) MD. The position in the sub-scanning direction (image vertical direction) SD determines whether the scanned row is the A field FA or B field FB.
FIG. 19B is a schematic diagram illustrating the interlace-scanning on the monitor 54. The A field FA constituted of a collection of odd rows is first scanned on the monitor 54, and then the B field constituted of a collection of even rows is scanned. One row is a train of pixels to be scanned in the main scanning direction (image horizontal direction) MD. A position along the sub-scanning direction (image vertical direction) SD determines whether the scanned row is the A field FA or B field FB.
It is an object of the present invention to provide a solid-state image pickup device and a charge transfer method capable of efficiently transferring electric charges accumulated in the solid-state image pickup device.
It is another object of the present invention to provide a solid-state image pickup device and a charge transfer method capable of efficiently transferring electric charges of thinned image signals.
It is another object of the present invention to provide an image signal processing apparatus and method capable of reading, at high speed, image signals of an image formed on a solid-state image pickup device.
According to one aspect of the present invention, there is provided a solid-state image pickup device comprising: a plurality of first transfer paths each having a plurality of transfer stages each capable of storing electric charges and transferring the electric charges in a first direction; a second transfer path having a plurality of transfer stages each capable of storing electric charges, receiving electric charges in the plurality of first transfer paths, and transferring the electric charges in a second direction; and charge transfer means for transferring electric charges of two packets or more stored in different transfer stages of at least one first transfer path among the plurality of first transfer paths, to different transfer stages of the second transfer path, and transferring the electric charges of the two packets or more in the second transfer path in the second direction by separating the electric charges of the two packets or more.
After the electric charges of two packets or more in each of the first transfer paths are transferred to the second transfer path, the electric charges in the second transfer path are transferred. Accordingly, as compared to the case wherein after the electric charges of one packet in each of the first transfer paths are transferred to the second transfer path, the electric charges in the second transfer path are transferred, a more efficient transfer of the electric charges in the second direction becomes possible because the number of empty transfer stages of the second transfer path reduces.
According to another aspect of the present invention, there is provided a solid-state image pickup device comprising: first transfer paths capable of transferring electric charges in a first direction; a second transfer path capable of receiving the electric charges in the first transfer paths and transferring the electric charges in a second direction; and drains for controlling whether the electric charges in the first transfer paths are to be transferred to the second transfer path by selectively draining the electric charges.
Whether the electric charges in the first transfer paths are to be transferred to the second transfer path can be controlled by selectively draining the electric charges. It is therefore possible to generate image signals with desired pixels being thinned.
According to another aspect of the present invention, there is provided an image signal processing apparatus comprising: a solid-state image pickup device capable of taking a two-dimensional image, the device having a plurality of primary transfer paths and a secondary transfer path, wherein the plurality of primary first transfer each have a plurality of transfer stages each capable of storing electric charges and transfer the electric charges in a first direction, and the secondary transfer path has a plurality of transfer stages each capable of storing electric charges, receives electric charges in the plurality of primary transfer paths, and transfers the electric charges in a second direction; read means for scanning the two-dimensional image on the solid-state image pickup device in a main scan direction corresponding to the second direction and in a sub-scan direction corresponding to the first direction and reading the electric charges in the secondary transfer path as image signals; and output means for outputting the read image signals on a monitor by interchanging the main scan direction and the sub-scan direction.
In the solid-state image pickup device, the smaller the number of primary transfer paths (horizontal pixels), the electric charges can be transferred at higher speed in the first direction, For example, a laterally long two-dimensional image, typically the NTSC format, has generally the number of horizontal pixels greater than the number of vertical pixels. A conventional solid-state image pickup device has the number of horizontal pixels greater than that of vertical pixels in conformity with the NTSC format or the like. In this invention, the number of horizontal pixels of a solid-state image pickup device is made greater than that of vertical pixels. It is therefore possible to read electric charges from the solid-state image pickup device at high speed without lowering the resolution. In outputting the image signals to a monitor, the main scanning and sub-scanning directions are interchanged so that a laterally long image of the NTSC format or the like having the number of horizontal pixels greater than that of vertical pixels can be displayed on the monitor.
According to another aspect of the present invention, there is provided an image signal processing method for a solid-state image pickup device capable of taking a two-dimensional image, the device having primary transfer paths for transferring electric charges in a first direction and a secondary transfer path for receiving the electric charges from the primary transfer paths and transferring the electric charges in a second direction, the image signal processing method comprising the steps of: (a) scanning the two-dimensional image on the solid-state image pickup device in a main scan direction corresponding to the second direction and in a sub-scan direction corresponding to the first direction and reading the electric charges in the secondary transfer path as image signals; and (b) outputting the read image signals on a monitor by interchanging the main scan direction and the sub-scan direction.